This invention relates to a low-cost packaging method which utilizes a commercially available High Density Multilayer Interconnect (HDMI or sometimes simply HDI) package and multichip interconnect for the integration of a novel 2-D reconfigurable antenna array with Radio Frequency (RF) Microelectromechanical (MEM) switches on top of a high impedance surface (High-Z Surface).
The prior art includes U.S. Pat. No. 5,541,614 to Juan F. Lam, Gregory L. Tangonan, and Richard L. Abrams, xe2x80x9cSmart antenna system using microelectromechanically tunable dipole antennas and photoic bandgap materialsxe2x80x9d. This patent shows how to use RF MEMS switches and photonic bandgap surfaces for reconfigurable dipoles.
The prior art also includes RF MEMS tunable dipoles xc2xc wavelength above a metallic ground plane, but this approach results in limited bandwidth and is not suspectible to convenient packaging.
The prior art further includes a pending application of D. Sievenpiper and E. Yablonovitch, xe2x80x9cCircuit and Method for Eliminatig Surface Currents on Metalsxe2x80x9d U.S. provisional patent application, Ser. No. 60/079,953, filed on Mar. 30, 1998 and corresponding PCT application PCT/US99/06884, published as WO99/50929 on Oct. 7, 1999 which disclose a high impedance surface (also called a Hi-Z surface herein).
The present invention takes advantage of proven, low-cost, high-density, multichip module (HDMI MCM-D) packaging. Such packaging is commercially available from Raytheon of El Segundo, Calif. under name/model number HDMI. FIG. 1 illustrates a cross-section of a prior art thin film copper/polyimide multilayer HDMI MCM-D integrated structure fabricated on a silicon substrate. As is known in the art, the fabrication process involves spin or curtain coating of xcx9c10-xcexcm-thick polyimide dielectric layers and sputter deposition of xcx9c10-xcexcm-thick copper conductor layers in an interactive process which includes phase mask laser formation of z-axis interconnect vias and metal patterning. Using comparable processes, more than 35,000 complex 2xe2x80x3xc3x974xe2x80x3 MCM-D modules have been built and used in airborne radar, military and commercial satellites, and space projectiles to meet demanding weight and volume requirements, with no reported field failures.
The substrate for this package used in the present invention is preferably either glass, quartz or silicon (Si). A Hi-Z is also provided. The dielectric for the Hi-Z surface is a polyimide layer which may have been originally used for the packaging. The antenna is placed adjacent the Hi-Z surface, and the RF MEMS switches are used to reconfigure the antenna simply by changing the dipole""s length. The feed structures for the antennas and dc lines are placed behind the Hi-Z Surface, so that they do not interfere with the radiation pattern of the antenna. The whole package is environmentally protected.
Preferably the Hi-Z surface utilized is a Hi-Z surface with added discrete inductors.
There is and has been a need for a packaged device of the type described above since it has a wide variety of applications in military and commercial communications requiring small reliable high performance antennas. One reason is that RF MEMS switches offer very low insertion loss ( less than 0.2 dB) and high isolation ( greater than 35 dB) over a very broad frequency range from dc to 40 GHz. Furthermore, they consume very little power (i.e. less than 200 pJ per activation). The High-Z Surface allows the antenna to be very compact. Finally, since the antenna is reconfigurable by means of the RF MEM switches, it can be made to operate at different desired frequencies.
In general terms, the present invention provides, in one aspect thereof, a method of making a thin, flexible antenna. According to this aspect of the invention, a layer of a flexible insulating medium is deposited on a substrate and patterning the layer of insulating medium to form openings therein. Thereafter, metal layers are deposited on a previously deposited insulating layer and patterned as needed and layers of a flexible insulating medium are deposited on the previously deposited metal layer and patterned as needed, the layers of metal and layers of insulating medium forming form a multilayered high impedance surface having an upper surface with antenna segments having been patterned from a metal layer previously deposited thereat, an array of metallic top elements formed in a layer spaced from the upper surface, the array of metallic top elements having been patterned from a metal layer previously deposited thereat, a metallic ground plane formed in a layer spaced from the array of metallic top elements, the metallic ground plane having been formed from a metal layer previously deposited thereat, and inductive elements coupling each of the top elements in the array of metallic top elements with the ground plane, the inductive elements having been formed from one or more metal layers previously deposited. Then optically controlled switches are disposed adjacent at least selected ones of the antenna segments for coupling the adjacent antenna segments together in response to light impinging a photovoltaic cell associated each optically controlled switch. Optic fibers are arranged on or adjacent the high impedance surface with distal ends of each optic fiber being coupled to a respective one of the optically controlled switches for coupling light carried by the optic fibre to the photovoltaic cells associated with the optically controlled switch. The multilayered high impedance surface from the substrate, the substrate simply providing a support for making the thin, flexible antenna during manufacture.